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Animal Bridges??

AJ Gall 6.15.2015

You may think the above image looks like a snapshot of a strange bridge taken straight out of the SimCity game, but this is real life in the state of Washington. What is it, you ask? It’s exactly what it looks like…a bridge for wildlife of all kinds to use to safely cross the road. In fact, there are many of these already in place throughout the world today as you’ll see below.

The image pictured above is an artistic rendering of a bridge over I-90 east of Snoqualmie Pass in Washington. The Department of Transportation broke ground on the project June of 2015. This overpass is part of a 15 mile stretch spanning along I-90 that is set to become one of the safest travel zones for wildlife and humans alike.

In Colorado, The Highway 9 Wildlife Crossing Project (pictured above) was designed to improve driver safety while allowing for wildlife movement across the road. You can get the full story on the project here.

This project includes:

two wildlife overpasses,

five wildlife underpasses,

nine pedestrian walk-throughs,

62 wildlife escape ramps,

29 wildlife guards, all of which are connected by an eight foot high wildlife fence.

While the images and thoughtfulness are intriguing, I have my own doubts as a biologist. First off, let me state that I’m all for helping wildlife safely utilize their entire range, and anything we can do in this man-made world to benefit wildlife is a good thing if the appropriate actions are considered. I first heard about these safe wildlife passages in a college biology class and pretty much have the same thoughts now as I did as a freshman bio student: Cool, but are they worth it?

First and foremost, citizens must be willing to cover the costs, which aren’t cheap. This single bridge is expected to cost $6.2 million and scheduled to open in 2019. I chuckle every time I hear “scheduled to open”, as if the animals will know when they can safely cross the interstate aboard the habitat bridge. Maybe they’ll post a sign for them to read “OVERPASS TO OPEN THIS MONDAY”. Alright, enough sarcasm for now, that price is nothing to joke about.

Secondly, do they work? I guess it depends upon what you classify as working. Does working mean one animal crosses it per day? Two animals? A herd? Big animals like deer and elk? Or small animals like frogs and spiders? Also, how many need to safely cross to deem it cost effective? One area that I would completely agree with placing these bridges on is along known migration routes that cross busy roads. There’s no doubt that animals do use them, as evident from trail cameras placed on currently operating wildlife bridges (check out the video below).

Thirdly, as a hunter, one thing jumps out to me immediately…they create the ultimate bottleneck or funnel. Let’s just say I know where I would be hunting if one of these were on my land or public hunting ground! However, there’s probably about 1,000 other hunters that would be thinking the same thing, but can you imagine sitting near such a funnel during the rut! Enough daydreaming . . . if we hunters are thinking about this ambush location, you can guarantee other predators are as well. If I’m not mistaken, I remember reading a scientific paper in college illustrating the effects these animal bridges had on predation, and I don’t recall a good outcome for species like deer and other ungulates. Think about it, these deer are basically walking into a cougars waiting claws. With that comes learned behavior. Eventually the deer and other animals will not cross these because they fear their life, which leads me to the next point.

These animal bridges function with the aid of some fencing. Basically, fencing stretches a certain distance from both ends of the bridge to create a barrier that deer cannot cross. This in essence, creates the bottleneck, it’s just like hunting a gap or open gate in a fence . . . the animal runs into this obstruction and then follows it until they can get through (the bridge). Now, let’s revisit the last point, predators have caused the prey to stay away from these crossings, and there is a giant fence. Now these animals are basically locked to their side of the interstate instead of crossing wherever they could. Some may argue that crossing the interstate may be more dangerous than the predator guarded bridges, but only time and science will tell. Also, it’s tough to factor in the true effectiveness if prey animals abandon the land bridges and are unable to seek out mates and resources on the other side. Genetic diversity comes into play, as do habitat resources, and home ranges.

Home ranges is an entirely different topic of discussion, but will undoubtedly be effected. Without diving completely into this sub-topic, let me leave you with this thought about home ranges. An average white-tailed deer has a home range of right around 1 square mile (640 acres) and a mule deer’s is slightly more. Now, if you’re not familiar with how home ranges for animals work, they are like a buried electrical fence for dogs, in the sense that deer rarely, if ever, leave them. So, depending upon the length of the extending fences and location of the actual bridge, only a certain percentage of wildlife will actually use them because they fall within their home range. These fences which span long distances, may now prevent travel across the interstate for animals who don’t have a bridge within their home range. Seems a bit counterintuitive, don’t you think? Not only this, but large predators like bears, cougars, and wolves have significantly larger home ranges, meaning their hunting grounds are much bigger and potentially allow them to cover multiple animal bridges.

Anyways, upon all my points, I still remain undecided on these structures. On one hand as a hunter and conservationist, I want to love them. On the other side as a pessimist, I’m not sure they are worth it – for wildlife or humans. Nonetheless, they are impressive structures and look quite odd from the sky, so I encourage you to take a look at some of these animal bridges below.

1. A wildlife bridge spans a busy interstate in the Netherlands.

2. Pictured below is an animal bridge in Banff National Park, Alberta.

3. Another view of an animal overpass in Banff, Alberta, Canada.

4. An animal overpass in Scotch Plains, New Jersey.

5. Another artistic rendering of a different overpass near Keechelus Lake, Washington.

6. Animal overpass on Novelty Hill Road in King County, Washington.

7. Another animal overpass in the Netherlands.

8. Animal overpass over a busy interstate.

10. An animal overpass in Germany.

11. A large habitat bridge spanning over a busy interstate to help animals cross safely.

12. An animal overpass on the Flathead Indian Reservation in Montana.

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About the Author

AJ Gall

AJ Gall is the Legendary Whitetails Community Page editor. His prior hunting and wildlife experiences began long ago and make him the perfect in-house expert. AJ acquired his degree in wildlife management and research from the University of Wisconsin-Stevens Point and immediately began working with his passion – white-tailed deer.